Fresnel lens is an optical lens designed to produce a thin, easily transported lens that can be made much thinner than a comparable conventional lens. It is commonly used in lighthouses, as well as in other applications such as telephoto lenses. There are some synonyms to the term Fresnel lenses that can be used to refer to this type of lens. These include Fresnel prism, Fresnel lens sheet, Fresnel mirror, and Fresnel surface. These terms are frequently used interchangeably, but all refer to the same essential idea of a lens that uses a series of concentric rings to focus light in a particular way.